The present invention concerns the problem of positioning and retaining conduits, for example electrical conductors, in contact with a surface, such as, for example, a shelf surface which is spaced apart from another shelf or other surface. For example, in pharmaceutical, biotechnological or food industries, validation and accountability of equipment are vital in view of strict standards applicable in these industries. Such equipment often comprises isolation chambers in which specific conditions, such as sterility, certain temperature or pressure levels, must be maintained during the manufacturing process or a part of it. Validation of such equipment involves introducing various electronic measuring devices to ensure that the equipment provides the required conditions. For example, in a lyophilization process, products are placed on a shelf within the isolation chamber of the lyophilizer. The products are initially frozen and then dried under vacuum while heat is transferred by thermal conduction from the shelves to the product. Accurate temperature and pressure values must be maintained in the chamber in order to achieve high quality products. For validation of lyophilisation equipment, series of thermocouples are employed in a plurality of locations within the chamber to measure the temperature of the shelves. Insulated wires of the thermocouples sealingly pass through a bulkhead which separates the surrounding atmosphere and the chamber. The measuring tips of the thermocouples are positioned in various locations in the chamber in contact with the shelf surfaces. Electric current produced by the thermocouples during measurements is very low and highly dependent on thermal conductivity between the tip and the shelf. It is therefore vital to maintain close contact of the measuring tips with the shelves throughout the validation process in order to register reliable measurements. In some applications, measurement tips of thermocouples are suspended above and/or below the shelves for taking and recording measurements of air temperature at various locations in the chamber. In this case it is necessary to ensure that the suspension state of a measuring tip of a thermocouple is maintained undisturbed throughout the validation process and that no contact between the measuring tip and a shelf surface or any other object within the isolated chamber occurs.
Many other processes, including but not limited to sterilisation processes, equally require validation of the internal condition in the isolation chamber by introducing thermally-responsive conductors into the chamber. In each case, it is necessary to ensure that working ends of sensors remain stationary and/or that thermal conductivity between working ends and examined surfaces remains constant.
Other examples of processes which may involve use of thermally-responsive conductors in an isolated chamber include processes such as heating of products in dry heat ovens, autoclaving or, indeed, freezing, steaming or pasteurisation processes.
Another problem related to placement of a sensor-tipped conductor into an isolation chamber is locating and fixing the sensor tip on a surface of a shelf, especially in a relatively inaccessible region of the surface.
A known approach to place and anchor a sensor tip of a conductor to a surface e.g. a shelf surface in a lyophilizer or an autoclave involves manually accessing the required location in the chamber and mere taping of the sensor tip to the shelf surface. Additionally or alternatively, a thermoconductive paste can be placed between the sensor tip and the examined surface. The disadvantage of such an approach is that the configuration of some isolation chambers renders them unsuitable for easy manual access. For example, in autoclaves the vertical distance between shelves is variable. In some typical application, this distance can be about 120 mm. The shelf size can be about 0.91 m by 1.52 m (3 by 5 feet) making it rather difficult for an operator to position and anchor a sensor tip of a conductor in the distal regions of the shelf surface. Another disadvantage of this known method is that tape does not always provide the required, reliable, effective contact between a sensor tip and a shelf surface, resulting in poor thermal conductivity and hence inaccurate readings. A still further disadvantage of this method lies in the necessity for cleaning shelf surfaces after a validation process cycle is complete so as to remove the adhesive and/or the thermoconductive paste which remains on the shelf surface after a sensor tip has been removed. This adds to the risk of compromising aseptic conditions which must be met for a particular process and also takes time during which the equipment is unavailable for use.
A thermocouple anchor is supplied by KRP Validation Services, Inc. of Manteno, Ill., United States of America for placing and retaining a sensor tip of a thermocouple on a shelf of a lyophilizer. The anchor is extendable between two shelves. It comprises two portions, each of which has a surface for bearing against a shelf, the portions being connected by a screw which is operable to adjust the distance between the bearing surfaces. One of the portions can receive a thermocouple. The anchor is placeable between the shelves and adjustable by the screw to retain the anchor between the shelves. A spring mechanism is also provided to permit fine adjustment so as to provide firm contact of the bearing surfaces with the shelves.
A disadvantageous feature of this device is that adjustment of the height of the anchor tool must be carried out prior to its placement between the shelves and must be accurate enough so as not to over-extend the device thus making positioning of the tool difficult. The tool is designed so that the adjusted height will only allow for holding the tool in place and will not provide sufficient pressure towards the sensor tip so as to maintain stable thermal conductivity between the tip and a shelf surface. Furthermore, positioning of the device between the shelves is carried out as the bearing surfaces slide along the corresponding shelf surfaces.
Another problem associated with such an anchor tool is that during cycles of a validation process, shelves of a lyophilizing apparatus are subjected to substantial thermal fluctuations between about −70° C. and +130° C. and therefore expand or contract in accordance with the change of temperature. This exerts undesirable effects on the performance of the anchor tool and in particular can compromise the effective pressure exerted on a conduit from the shelf surface and the clamping piece between which the conduit is retained.
U.S. Pat. No. 4,527,005 (McKelvey et al) discloses a spring-loaded thermocouple module which includes a cup-like holder in which an insulation member is movably received. The insulation member further has passages for receiving a pair of thermocouple wires which join together into a weld bead outside the insulation member. A spring is loaded into the cup-like holder to be held captive within the holder and the spring is operable to apply a bias force to the weld bead through the insulation member. The cup-like holder has a thread on its outside surface for threading the holder into a blind opening of a specimen. When the holder is installed in the specimen, the weld bead is held in contact with the end wall of the blind opening of the specimen by the bias force of the spring.